1. Field
The disclosure relates to machines and methods used in powder-based additive manufacturing by sintering or melting particles of the said powder using a beam of energy, such as an electromagnetic radiation (for example a laser beam), or a beam of particles (for example an electron beam). Such a powder-based additive manufacturing method leads to a successive, layer by layer, consolidation, using a beam of energy or particles, of the selected zones of a stratum of pulverulent material, the consolidated zones corresponding to successive sections of the three-dimensional object.
More specifically, the disclosure relates to the means and methods used for transferring a three-dimensional object between an additive manufacturing workstation and a workstation for the removal of the manufactured object, more particular of the type employing an interchangeable container in which the manufactured object is situated.
2. Description of Related Art
Document WO 90/03893 describes a machine for the manufacture of a three-dimensional object by successive, layer by layer, consolidation, using a laser beam, of a pulverulent material, which uses a mobile container. The container contains the object-support plate and means for driving the vertical translational movement thereof. The container is moved along horizontal rails between the workstations for the deposition, the spreading and the compression of the powder, and the workstation at which the prepared layer of powder is treated with the laser beam. The disadvantages of this solution are connected with the fact that the object is manufactured inside a container which additionally contains the drive means, which means that it is heavier, bulkier and therefore more difficult and more expensive to transport. On top of that, this container needs to be positioned very precisely facing each workstation of the machine, because if it is not, there is a risk that errors in the geometry of the manufactured object will appear.
Document U.S. Pat. No. 6,554,600-B1 discloses another example of a machine allowing the manufacture of a three-dimensional object by sintering powder using a laser beam. This machine comprises a build space within which is arranged an interchangeable container comprising a build envelope and a platform for supporting the object that is to be manufactured. The object that is to be manufactured is built inside the container which is then removed from the build space at the end of the operation. In an alternative form, the container, in addition to containing the platform and the object that is to be manufactured, contains a mechanism for the support and translational movement of the platform. The disadvantages with this configuration are the substantial bulk and weight of the container that is to be transported. In another alternative form, the rear wall of the container comprises vertical slots through which means of attachment of the platform to a lateral arm that actuates the vertical translation thereof fit and slide. The disadvantage with this configuration is that it calls for the plate to be actuated in cantilever fashion, which places a great deal of stress on the actuating arm, particularly when the powder is being compressed or when components of large dimensions are being built. Moreover, complex sealing means need to be arranged at the vertical slots in order to prevent powder from escaping out of the container. On top of that, detaching the platform from the container and mounting a new platform are operations that are fairly tricky, as the platform needs to be positioned very precisely with respect to this container.
Document U.S. Pat. No. 7,204,684-B2 has proposed a solution in which the platform that bears the object that is to be manufactured is mounted via a support frame inside an interchangeable container. The platform is moved vertically driven by the hooks of an actuating device situated outside of the container and which comes into contact with the platform by passing through vertical channels made in the lateral walls of the container. In order to prevent powder from the container from contaminating the space outside the container, staged sealing means are provided at the periphery of the support frame. The frame thus comprises a metal blade surmounted by a felt seal that seals at each vertical channel. Leaving aside the fact that it is actuated by a cantilever system as in the preceding document, this configuration has a further disadvantage regarding the friction caused by such an enhanced sealing system that increases the thrust load of the platform actuating device.
Document U.S. Pat. No. 6,824,714-B1 describes another configuration for a machine for the additive manufacture of a powder-based object using laser sintering, the machine comprising a mobile container which is brought into the working zone by a chain conveyor. The container forms a build envelope for the object and contains the platform that supports the object. Because it forms the build space for the object, the container needs to be produced with great precision. The machine moreover comprises means of coupling between the mobile container and a tank of the working zone, and between a vertical actuator independent of the container and the support platform. In order to allow the container to be positioned correctly within the working zone of the machine, these coupling means call for precision mechanisms which can operate only if there is very good sealing between the container and the plate. This is because if powder particles contaminate the container and plate locking mechanisms, these mechanisms would become inoperative.
One problem that the various proposals have in common is the need for a high degree of precision in the creation of the interchangeable container. This is because since the object is produced actually within the container, this container requires very tight manufacturing and assembly tolerances, thereby increasing the cost of manufacturing it.
An additional problem is that of the fouling of the machine by powder particles when an object is being manufactured. One solution has been proposed in the above-mentioned document WO 90/03893, notably because the machine incorporates an extraction device that sucks up powder residue that remains after the layer of powder distributed over the working zone has been compacted. However, such extraction performed prior to the melting carries the risk of dislodging particles from the layer of powder already prepared and increases the time taken to manufacture the object.
Elsewhere, document DE 10 2006 032 025 describes a powder-based additive manufacturing machine in which the frame that forms the build space of the object within the chassis of the machine can be reduced to the dimensions of an object smaller than initially anticipated by mounting a build sleeve on the chassis and combining with it pistons of corresponding size. That document does not describe a mobile container for transporting the object, and, as a result, the operations of loading and unloading the object are laborious.
Another solution for modifying the work space is described in document DE 10 2010 020 416 and, in the absence of a mobile container for transporting the object, it presents the same disadvantages as the preceding document.
Documents WO 2007/003244 and DE 10 2009 015 130 themselves describe mobile containers that allow the transport of the object which has been manufactured in a powder-based additive manufacturing machine. The container forms a build envelope for the object that is to be manufactured and, as a result, the container needs to be produced very accurately, with very tight tolerances. In addition, the container contains the means for the vertical movement of the build plate of the object, making transport operations less easy.